PM56725: DB2 V10 INCREASE IN DBM1 TCB TIME AND OPEN/CLOSE ACTIVITY

A fix is available

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APAR status

Closed as program error.

Error description

Increase in DBM1 TCB times and dataset open / close activity
after migrating to DB2 v10 CM9.

Local fix

N/A

Problem summary

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* USERS AFFECTED: DB2 users. *
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* PROBLEM DESCRIPTION: Excessive dataset open/close activity, *
* resulting in increased CPU time for the *
* DBM1 address space. *
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* RECOMMENDATION: *
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The deferred close process (responsible for closing excess data
sets when DSMAX has been exceeded) builds a large candidate list
which it may continue using for a long period of time (several
hours). Since this list is ordered by last-referenced time at
the time the list was built, and the closing of candidates does
not check to see if the reference time has changed, the order
of closing datasets becomes less and less an LRU process the
longer the list remains active. This may result in incorrectly
closing datasets which are currently being frequently accessed,
rather than others which are not currently being used. This
may be particularly noticable if the list is built while one
type of workload is being run (e.g. overnight batch jobs) but
is still being used while another type of workload is being
run (e.g. daytime online transactions).

Problem conclusion

The deferred close process has been modified to skip datasets
on its candidate list which have been referenced since the time
the list was built.